High-intensity focused ultrasound (HIFU) is mainly used for treatment of malignant tumors. It has many clinical features: it can realize noninvasive or minimally invasive surgery; it has more sensitive destruction effects on anaerobic tumor cells; it has indiscriminate treatment effects for proliferative and non-proliferative tumors (liver tumors and kidney tumors, etc.), and can induce specific immune responses of the body against tumors. However, the existing HIFU technique encounters a bottleneck problem when it is used to treat deep seated tumors, infracostal hepatic tumors, and large tumors. It is not because that the HIFU can't achieve high intensity focused ultrasound. For example, when the working frequency of HIFU is f=1.5 MHz, only sound power PA0≈150(W) is required to obtain focused sound intensity IF0≈15,000 W/cm2 in a free sound field. However, owing to the natural thermal conductivity and blood supply of human body's tissues, the target area dissipates heat as the HIFU heats up.
From the mean parameters of known acoustical and biophysical of human body's soft tissues, it is easy to know (by means of experimentation and computer simulation) that the mean maximum effective therapeutic depth (maximum focus-skin distance) of niduses in subcutaneous soft tissues by HIFU is only several centimeters. In addition, the treatment speed is very low. Even for a medium-size nidus, the time required for treatment is intolerable. Doing research on a technique that can reliably emit KW-level HIFU with dominant focus performance is a key for truly achieving the “one-off noninvasive surgery” concept with HIFU. Therefore, the measurement of KW-level ultrasound power is an indispensable and key link for research and development, production, actual application, detection and diagnosis, and maintenance of high-intensity focused ultrasound (HIFU) equipment.
With reference to relevant literature, Nanjing HAIKE Medical Equipment Co., Ltd. designed a coeloconoid reflection target that is made of metal materials and can measure KW-level HIFU power. Experiments have shown that such reflection targets can't ensure the sound beams emitted by HIFU transducers with different physical structures meet necessary total internal reflection conditions of longitudinal and transverse waves at the target; therefore, the authenticity is surely doubtful if the sound power of the radiation source is calculated from the measured sound radiation power.
At present, most methods used domestically and abroad for measuring power of high-power and high-intensity focused ultrasound calculate the sound power emitted from the sound source by measuring the normal radial force which acts on the absorption target, so does the method recommended in the national standard of China (GB/T19890-2005). However, at present, only absorption targets for measuring sound power at 100 W level are practical, and they can't meet the present and future demand for HIFU.